Method and equipment for extrusion

ABSTRACT

A method for extrusion molding and equipment for carrying out the method is disclosed in which, prior to extrusion, porous blocks are compressed such that the density gradually increases from the interior to the exterior to force enclosed gas to flow in outward directions.

United States Patent [191 Wessel Apr. 9, 1974 METHOD AND EQUIPMENT FOR [56] References Cited EXTRUSION UNITED STATES PATENTS Inventor: Otto Wessel, Duisburg-Ungelsheim, 3,483,597 12/1969 Windeler 425/373 Germany 1,664,990 4/1928 Oehmig 72/265 [73] Assignee: Mannesmann Aktiengesellschaft, Y

D ld f Germany Primary Examiner-Charles W. Lanham Assistant Examiner-Robert M. Rogers [22] Flledi 1972 Attorney, Agent, or Firm-Smyth, Roston & Pavitt [21] App]. No.: 215,885

Related US. Application Data [57] ABSTRACT [62] Division of Ser. No. 818,023, April 21, 1969, A method for extrusion molding and equipment for abandoned. carrying out the method is disclosed in which, prior to extrusion, porous blocks are compressed such that the [52] US. Cl. 72/256, 72/377 density gradually increases from the interior to the ex- [51] Int. Cl. B21c 23/00 terior to force enclosed gas to flow in outward direc- [58] Field of Search 72/256, 265, 271, 700, ti

5 Claims, 3 Drawing Figures PATENTEBAPR 9 I974 3,802,243

SHEET 2 [1F 2 Fig.3 4

METHOD AND EQUIPMENT FOR EXTRUSION This is a division, of application Ser. No. 818,023, filed Apr. 21, 1969 now abandoned.

The present invention relates to method and apparatus for extrusion such as extrusion molding of work pieces having hollow or solid sections at rather high density, while using porous blocks as raw material and which, in turn, have been manufactured from powdery material. The invention, furthermore, relates to equipment coacting with such a block on basis of particular contour relationship including novel aspects for the blocks themselves.

In the recent past, it has become known to use metallic powder for extrusion molding. In particular, the powder is preformed or pressed into blocks and the blocks are extruded. The resulting reaction pressure arising during extrusion was found to be particularly favorable, and the degree of possible deformation is particularly high when such porous blocks are used as raw material. The extrusion is conducted at cold temperatures. However, the temperature should preferably be above the recrystallization temperature of the material.

It was found, however, that certain difficulties arise if one attempts to extrude directly from porous blocks for producing a rather compact final product. These difficulties arise particularly from the gases encapsuled in the pores or lodged between the grains of the powder. As a ram or plunger exerts pressure upon the powder, or the porous blocks which have been placed in the receiver portion of the extrusion apparatus, there is at first an increase in density, i.e., the compression reduces the porosity. Subsequent thereto, the compressed material begins to flow for extrusion through the extrusion nozzle of the die.

Gas still remaining in pores and cavities is very strongly compressed, and pressure therein may rise up to 5,000 or even as high as 15,000 atmospheres, depending upon the material that is being worked. This, of course, is true only if the gas could not escape. In case of large, porous blocks having relatively low relative density, considerable quantities of gas have to be removed, but usually only comparatively short periods of time are available for the gas removal. Moreover, the gas is to be removed under highly unfavorable flow conditions because the cells and pores establishing the porosity have rather small dimensions, establishing long and narrow flow paths. Moreover, extrusion molding equipment as commonly used has rather close tolerances so that further escape of gas is impeded, even inhibited.

The gas encapsuled in the pores has usually been used for heating. This gas as enclosed in the pores and compressed is heated during the compression, particularly after hot extrusion or during a subsequent heating process. This, in turn, may cause the extruded material to tear and to form enclosed bubbles in the final product.

It is now known to avoid the inclusion of gas during extrusion molding in that the porous blocks are clad in a sheet metal lining. The lining is closed through welding, and the resulting enclosure is finally hermetically sealed. Thus, the porous blocks are degassed prior to extrusion. The metallic lining is likewise extruded and protects the block against gas and lubricants from the outside. However, such a method is necessarily rather expensive and is particularly not economical for easily reducible materials such as copper, nickel or iron.

Another way to avoid gas enclosure is known and is disclosed in British Pat. No. 1,008,250. According to this known method the blocks are formed with a rather low total volume of the pores. In accordance with the teaching of that British patent, the porous blocks are made from powder, preferably having grains of the size of 0.01 through 0.012 millimeters. The resulting blocks have a rather uniform, relative density of 80 to 90 percent. The principal difficulty with this method arises from the fact that treatment of such porous blocks with a gas down to the core, for example, a reduction of oxides in a gaseous atmosphere is practically not possible economically as for such high densities the gas treatment requires too much time.

It is an object of the present invention, to provide a method and equipment for extrusion molding without incurring gas enclosures in the final product while using porous blocks without outer lining or cover from which to extrude. In accordance with the invention, it is suggested to use uncovered blocks of open porosity and having a relative density of 50 to percent and to compress such a block prior to extrusion flow of the material such that the density increases progressively from the interior toward the outside. In particular, the block is compressed by applying force in a particular direction along a central axis of such a porous block, and the density is made to increase in radial outward progression from the axis along which the force applying plunger moves.

The block and/or the plunger are appropriately shaped to obtain compression at gradual progression from the interior towards the outside to force the gas out of compressed pores and into pores not yet or less compressed. Hence, the gas is forced to flow in radial outward direction, corresponding to the progression of the compression. In general, the invention resides in the providing of a controlled rate and spatial distribution of compression such that the enclosed gas is forced to flow in the desired direction to be finally forced out of block and tool.

As compression is continued, the material extrudes without carrying gas bubbles. The inventive method regarding the essentially radially progressing compression of the block can be practiced, for example, by perforating a solid block or by enlarging or widening a hollow block in the extrusion molding equipment. The final product will then have hollow section.

The invention includes equipment for manufacturing dense and solid or hollow section pieces by means of extrusion molding from porous, uncovered blocks made of powdery material. Plunger and die member of the extrusion press have surfaces which face each other across the receiver cavity holding the block. These surfaces are relative inclined to each other with reference to an axis. As preferred construction, the plunger head is provided with a convex contour established, for example, by a conical or frustoconical protrusion. The die member is provided with a concave contour established, for example, by a conical or frustoconical indentation. Generally, the concave identation is to be shallower (even completely flat) than the convexity by which the plunger head protrudes.

The extrusion press equipment is characterized in particular in that die member and plunger have frustoconically-shaped surfaces facing each other across the receiver, whereby the base angles differ by approximately to 30 percent; the base angle of the plunger head surface being the larger one. Preferably, the base angle of the frustoconical protrusion of the plunger is larger by 17 to 22 than the base angle of the coacting die member. The base angle of the frustoconical indentation of the die member itself may have an angle in the range of 0v to preferably 10.

The difference in relative inclination of the coacting surfaces of plunger and die member causes force to be applied upon the porous blocks at first in a core zone along the axis of relative motion of plunger and die member. Hence, that central axial region of the porous block is compressed first. As compression pressure continues, the compression propagates from this central region in an outward direction. Gas contained in the pores is forced to escape corresponding to the progressingcompression from the inner region toward the outer regions of the block.

The gas will collect near the outer, circumferential surfaces of the block, and in accordance with an additional feature of the invention the guiding surface for' the plunger which slides along the receiver and closes the receiver cavity, is provided with shallow grooves. The collected gas can escape through these grooves and along the adjacent walls of the receiver. As pressure is increased upon the block, the gas is forced into these grooves. In accordance with another feature of the present invention, the outer surface of the die member engaging the receiving section of the extrusion molding equipment may likewise be provided with shallow grooves for removal of gas in an analogous manner.

For extrusion of a work piece having hollow profile, the plunger arrangement is provided with a mandrel as known, per se. The purpose thereof is to perforate the block inside of the extrusion equipment. In accordance with this feature of the invention, the mandrel is provided with a conical peak having an apex angle of 45 to 75. Itwas found that best results can be obtained if the angle is about 60.

.The principle underlying the invention requires a compression gradient from the interior to the exterior of the compressed block prior to extrusion. This pressure gradient is obtainable through the particular angular relation between the two surfaces of plunger head and die member facing each other across the receiver cavity. However, it has to be observed that these two coacting surfaces engage different surface portions of the block. Therefore, the desired compression gradient can also be produced by an appropriate relationship between the block surfaces on one hand, and the two coacting surfaces of plunger head and die member.

It is, therefore, within the scope of the invention to produce the desired pressure distribution during compression in such a manner that the porous block is provided with at least one outwardly bulging front face. The bulging surface may preferably have the contour of a calotte. However, it is still preferred to provide the front face of the block with a frustoconical configuration. The base angle of this frustoconical protrusion of the block is preferably 10 to 30. It was found to be particularly advantageous to preshape the block as a cylinder (possibly with at least one frustoconical or calotte-shaped axial end face), and to choose the geometrical dimensions thereof such that the ratio of cylinder height to diameter is at least 25:1.

It should be mentioned that Britsh Pat. No. 1,008,250, referred to previously, basically discloses a plunger with a bulging head as well as a die with a particular inclination of its coacting surface. However, in this patent the several surfaces are inclined relative to each other such that a compression distribution results in which higher densities progress from outer to inner regions, therefore causing the gases to be firmly enclosed in the interior with little chance to escape.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features, and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is an elevation and cross section view of a device for making hollow section work pieces in accordance with the preferred embodiment of the present invention;

FIG. 2 illustrates an elevation and section view of a device for making solid section work pieces in accordance with the method of the present invention; and

FIG. 3 illustrates a block as it is to be used preferably for practicing the method in accordance with the present invention.

The device and equipment illustrated in FIG. 1 comprises a base plate 13 having a bore 23 receiving the extruded material. Plate 13 supports the receiver 9, as well as the member 5, provided with the extrusion nozzle 51. Receiver 9, die member 5 and a plunger head 2, when inserted in the receiver, define the receiver cavity. The receiver contains a block 6. Block 6 is presumed to have been prepressed from powdery material and constitutes a porous block having relative density of 50 to 80 percent, preferably 65 to percent.

A plunger 3 is provided above the block 6. The plunger 3 carries the head 2 having a frustoconicallyshaped protrusion 1 to define a press surface of like designation. Thus, a frusto-conically-shaped press surface faces the block 6, and through the receiver cavity the die member 5. A guiding surface 10 of plunger head 2 is provided with flat grooves l l for permitting escape of the gas which has been squeezed out of the block 6. The gas escapes from the receiver cavity through grooves 11 along adjacent, upper portion of the wall of receiver 9. The die member 5 is likewise provided with flat grooves 12 facing the lower wall portion of receiver 9 to permit the escape of gas.

The surface 4 of die member 5 defining the contour of the bottom of the receiver cavity is funnel or conically-shaped, i.e., the die member has a concavity defined by surface portions which are inclined toward center and extrusion nozzle 51, to likewise constitute a frustoconical surface.

The frustoconical protrusion surface 1 has a base angle a, measured relative to an axial plane, the axis of the core being the common axis of the system defining also the direction of plunger movement and running through the center of the extrusion nozzle and of the core defined by surface 4. The frustoconical surface 4 has a base angle [3 relative to another axial plane. In accordance with the principle of the invention, the base angle a is larger than the base angle ,6 the difference being in the range between 10 and 30. It is preferred to have a difference of l7-22. The base angle B itself is preferably between 0', and 15, an angle of about being preferred. Hence, in preferred configuration angle a has value between 27 and 32.

The plunger 3 is provided in its interior with a mandrel 7 which is concentric to frustoconical surfaces 1 and 4. Mandrel 7 is provided with a conical peak 8 in order to provide block 6 with a central bore or if the block does already have a central bore to widen the bore, the apex angle of that peak, y, is approximately 60. FIG. 1 illustrates mandrel 7 in a position of initial insertion into block 6. The dashed lines 7', 8, respectively, show mandrel and peak in protracted position after perforation or widening.

In FIG. 2 similar parts are designated by like reference numerals. The embodiment of FIG. 2 differs from the embodiment illustrated in FIG. 1 in that the former is designed to extrude a string or rod of solid section, while the latter produces hollow section work piece such as a tube. Aside from the difference in purpose, the plunger in FIG. 2 has a head 2' with a flat, downwardly directed press surface 1. The block 6' here is presumed to have frustoconical axial faces 14. Another block usable is shown separately in FIG. 3, having a calotte-shaped, lower surface 14. In either case, whether provided as calotte or as frustoconical protrusion, these axial convexities of the block have base angle 6 which is about 10 to 30. Moreover, the ratio of diameter d) to height H of the cylindrical block is 1:25 at the most.

As one can see, in either embodiment, as the plunger is lowered, the compression exerted upon the block 6 commences in the central region along an axis colinear with the direction of motion of the plunger. Basically, that axis is defined as the center of the region of initial compression. There is an initial compression all along the thus defined central core region resulting in a corresponding radial gradient of density. As the pores in this axial region of block 6 are squeezed more, gas is forced to flow into regions in which the pores have been squeezed less. The gas flow follows the resulting radial compression differential, i.e., the gas encapsuled in the pores of block 6 flows from regions of higher density to regions of low density, i.e., from regions of diminished pore volume to regions of less pore volume, which is in radial outward direction.

As the plunger moves down farther, compression continues to propagate radially outwardly from the inner core region of block 6 in outward direction until the material begins to flow for extrusion. The surprising effect is that even if the block has initially a rather high porosity, the gas is pressed out of the block and particularly out of the extruded material to such a degree that a homogeneous, bubble-free work piece can be extruded, either having a hollow section profile as in the equipment shown in FIG. 1 or a solid section profile as in FIG. 2.

A comparison of FIGS. 1, 2 and 3 reveals that the angle relationships as between the several surfaces involved can be established differently with similar results in principle. This includes the possibility of including in the overall consideration, the surface configuration and the material distribution in the block along the contemplated axis of plunger movement. Essential is that inner regions of the block such as an axial core thereof is compressed prior to compression of peripheral regions. The block contour can be directly instrumental in this operation of the extrusion press and in that sense must be regarded as a part thereof. In general then, this result can be obtained if the base angles of the several convex projections of plunger and block relative to axial planes are added together (counting flat surfaces as having zero base angle) and if the base angle (or angles) of concave indentations along the axis are subtracted from the sum of the base angles of convex projections. The difference must be positive to obtain the desired radial compression gradient for forcing the encapsuled gas to flow radially outwardly.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

I claim: 1. Method for extruding material, comprising the steps of:

providing a porous uncovered block made of powdery material, having relative density of about 50 to percent or thereabouts, and having first and second oppositely facing surfaces, the first one for facing the bottom of a die, the second one for facing a plunger as coacting with the die;

compressing the block in an internal region along an axis so that the compression progresses through the block in radial outward direction from said axis to the periphery of the block, to degas the block; providing for gas flow along the periphery of the block in axial direction; and

continuing to compress the block for providing extrusion flow to form a particular product at a particular profile.

2. Method as in claim 1, including using a die member with particular bottom surface and a plunger, for compressing the block, selected so that the angle between plunger face and the second block surface, at least in the vicinity of the periphery, is larger than the angle between the first block surface and the die member bottom surface, also at least in the vicinity of the periphery, so that compression of the block in axial direction is distributed for progressing radially outwardly.

3. Method as in claim 2, wherein the angles differ by 10 to 30 percent.

4. Method as in claim 1, including perforating the block as provided prior to compressing.

5. Method as in claim 1, including widening the block prior to compressing. 

1. Method for extruding material, comprising the steps of: providing a porous uncovered block made of powdery material, having relative density of about 50 to 80 percent or thereabouts, and having first and second oppositely facing surfaces, the first one for facing the bottom of a die, the second one for facing a plunger as coacting with the die; compressing the block in an internal region along an axis so that the compression progresses through the block in radial outward direction from said axis to the periphery of the block, to degas the block; providing for gas flow along the periphery of the block in axial direction; and continuing to compress thE block for providing extrusion flow to form a particular product at a particular profile.
 2. Method as in claim 1, including using a die member with particular bottom surface and a plunger, for compressing the block, selected so that the angle between plunger face and the second block surface, at least in the vicinity of the periphery, is larger than the angle between the first block surface and the die member bottom surface, also at least in the vicinity of the periphery, so that compression of the block in axial direction is distributed for progressing radially outwardly.
 3. Method as in claim 2, wherein the angles differ by 10 to 30 percent.
 4. Method as in claim 1, including perforating the block as provided prior to compressing.
 5. Method as in claim 1, including widening the block prior to compressing. 